His strong Roman instinct calls him back to recognise the paramount claims of daily life; and he is nowhere more himself than when he declares that every one would leave philosophy to take care of herself at the first summons of duty. [65] This subordination of the theoretical to the practical led him to confuse in a rhetorical presentation the several parts of philosophy, and it seeks and finds its justification to a great extent in the endless disputes in which in every department of thought the three chief schools were involved. Physics (as the term was understood in his day) seemed to him the most mysterious and doubtful portion of the whole. A knowledge of the body and its properties is difficult enough; how much more unattainable is a knowledge of such entities as the Deity and the soul! Those who pronounce absolutely on points like these involve themselves in the most inextricable contradictions. While they declare as certainties things that obviously differ in the general credence they meet with, they forget that certainty does not admit of degrees, whereas probability does. How much more reasonable therefore to regard such questions as coming within the sphere of the probable, and varying between the highest and the lowest degrees of probability. [66] In his moral theory Cicero shows greater decision. He is unwavering in his repudiation of the Epicurean view that virtue and pleasure are one, [67] and generally adheres to that of the other schools, who here agree in declaring that virtue consists in following nature. [68] But here occurs the difficulty as to what place is to be assigned to external goods. At one time he inclines to the lofty view of the Stoic that virtue is in itself sufficient for happiness; at another, struck by its inapplicability to practical life, he thinks this less true than the Peripatetic theory, which takes account of external circumstances, and though considering them as inappreciable when weighed in the balance against virtue, nevertheless admits that within certain limits they are necessary to a complete life. Thus it appears that both in physics and morals he doubted the reality of the great abstract conceptions of reason, and came back to the presentations of sense as at all events the most indisputably probable. This would lead us to infer that he rested upon the senses as the ultimate criterion of truth. But if he adopts them as a criterion at all, he does so with great reservations. He allows the senses indeed the power of judging between sweet and bitter, near and distant, and the like, but he never allows them to determine what is good and what is evil. [69] And similarly he allows the intellect the power of judgment on genera and species, but he does not deny that it sometimes spins out problems which it is wholly unable to solve. [70] Since therefore neither the senses nor the intellect are capable of supplying an infallible criterion, we must